Oseltamivir

Oseltamivir, commonly marketed under the trade name Tamiflu, is a prescription antiviral medication used in the treatment and prevention of influenza A and influenza B (flu) infections caused by influenza A and influenza B viruses. It belongs to a class of drugs known as neuraminidase inhibitors and works by blocking a key viral enzyme, thereby reducing the spread of the virus within the body.

---

Overview

Oseltamivir phosphate is an orally administered prodrug that is rapidly absorbed from the gastrointestinal tract and converted in the liver to its active metabolite, oseltamivir carboxylate. The active compound selectively inhibits the neuraminidase enzyme on the surface of influenza viruses, decreasing release of newly formed virions from infected cells and reducing the spread of infection.

It is most effective when given within 48 hours of symptom onset and is also approved for post-exposure prophylaxis in individuals exposed to influenza.

---

Medical Uses

Treatment of Influenza:

Oseltamivir is indicated for the acute, uncomplicated treatment of influenza A and B in patients aged 2 weeks and older who have been symptomatic for no more than 48 hours.

Prophylaxis:

It is also approved to prevent influenza following known or suspected exposure in children aged 1 year and older when influenza virus is circulating.

---

Mechanism of Action

Oseltamivir targets the viral neuraminidase enzyme, a glycoprotein essential for viral replication. By mimicking the natural substrate of neuraminidase, the drug blocks the enzymatic cleavage of sialic acid residues. This inhibits release of new virus particles from infected cells, slows viral spread, and reduces viral shedding and symptom duration.

---

Pharmacokinetics

• Absorption: High oral bioavailability with rapid uptake.
• Metabolism: The prodrug is converted to active oseltamivir carboxylate by hepatic and intestinal esterases.
• Elimination: The active metabolite is primarily excreted via the kidneys, with a half-life of approximately 6–10 hours.

---

Dosing

Dosing varies by age and indication:

• Adults (treatment): 75 mg orally twice daily for 5 days.
• Adults (prophylaxis): 75 mg once daily for at least 7 days after exposure.
• Pediatric dosing: Weight-based regimens are used for children under 15 kg.

Dosing adjustments may be required in individuals with reduced kidney function.

---

Side Effects and Safety

Oseltamivir is generally well-tolerated. The most common adverse effects include:

• Gastrointestinal: Nausea and vomiting (often mild and transient).
• Neurological: Headache, dizziness.
• Less common: Diarrhea, insomnia, vertigo.

Rare but serious reactions, including allergic skin reactions and neuropsychiatric events, have been reported.

---

Resistance

Influenza viruses can develop resistance to oseltamivir due to mutations in the neuraminidase enzyme. Resistant strains, especially certain influenza A subtypes (e.g., H1N1), have been documented, which may reduce effectiveness in some outbreaks.

---

Controversies & Evidence

The overall clinical benefits of oseltamivir — particularly in otherwise healthy populations — have been a subject of debate. Some analyses have questioned the magnitude of its effect on hospitalizations and serious complications, though public health agencies continue to include it as a tool for treatment and prevention in specified settings.

---

See Also

• Neuraminidase inhibitor
• Influenza antiviral therapy
• Tamiflu

---